Java: Why is this a Deadlock when lock is null?

I was having a deadlock scenario in my code. I reproduced the scenario with the following test code (look at the line number comments too).

I have one ExecuterService which takes 3 tasks, 2 tasks have a synchronized block over the same object which is not initialized it should have the null value.

synchronized(null){} is not allowed in java so I was expecting an error at line-2. However, this executed with a deadlock. i.e. the first two tasks were kept waiting by the 3rd task. (see Output-1)

Now If I change line-1 to Object lock = new Object(); The code will work flawlessly without any deadlock(Output-2). I am just wondering what exactly is happening with JVM when we provide an uninitialized mutex object? Looks like JVM is creating a static copy for the same, which shared by all the tasks. Hence the deadlock

public class Test {
    Object lock; //line -1
    Integer a = 10;

    public static void main(String[] arg) {
        new Test().doIt();
    }

    public void doIt() {
        ExecutorService service = Executors.newFixedThreadPool(3);

        service.submit(new Runnable() {
            public void run() {
                synchronized (Test.this.lock) { //line -2
                    try {
                        Thread.sleep(1000 * 5);
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                    Test.this.a = (int) Thread.currentThread().getId();
                    System.out.println(a + " " + Thread.currentThread().getId());

                }
            }
        });

        service.submit(new Runnable() {
            public void run() {
                synchronized (Test.this.lock) {
                    try {
                        Thread.sleep(1000 * 5);
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                    Test.this.a = (int) Thread.currentThread().getId();
                    System.out.println(a + " " + Thread.currentThread().getId());

                }
            }
        }

        );

        service.submit(new Runnable() {
            public void run() {
                Test.this.a = (int) Thread.currentThread().getId();
                while (true) {
                    try {
                        Thread.sleep(1 * 1000);
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                    System.out.println(a + " Main");
                }
            }
        });

    }
}

Output -1

11 Main
11 Main
11 Main
11 Main
11 Main
11 Main
11 Main
11 Main
11 Main
11 Main
11 Main
.
.
.

Output-2

11 Main
11 Main
11 Main
11 Main
9 9
9 Main
9 Main
9 Main
9 Main
9 Main
10 10
10 Main
10 Main
.
.
.